Frozen Mine
Action - Reaction
You may trash a Treasure you have in play, or in your hand, to gain a Silver to your hand.
----
When you gain a card, you may play this from your hand to set that card aside with 4 Ice tokens on it.
A mini-Mine that has some utility. Early game it upgrades your Coppers to Silver, later it freezes Green and Junk to keep the deck clean. Probably not a card I would ever buy more than one of. Feedback is welcome.
This seems too cheap. It can mostly mimic the benefits of a mine while providing some benefit in the later game. Also, you probably don't need the in play clause because it's very rare to have treasures in play during action phase (mine just allows trashing from hand).
You do need the "in play" because of the reaction that lets you play it when you gain a card.
But I also agree that it's too cheap. I would think it needs to cost at least $4. Otherwise it's almost a no-brainer to open with 2 of them.
Now that you mention it's not exactly clear how the reaction works. If I gain a card, can I play frozen mine for free (and trasha treasure for a silver) and freeze the gained card? This just makes it even more powerful.
Yeah pretty sure that's what it means; it's the reason it allows you to trash from in-play; because when you gain a card normally during your buy phase, you'll play this from hand to trash a Copper that you had played.
But early on, when you're more likely to have Copper in play, you don't want to freeze your incoming card. So freezing the card is a penalty, but it's awkward because normally "you may do X to do Y" is used when Y is something you want to do, and X is the price you have to pay to do it. Here, it's the opposite... you want to do X, but doing so would force you to also do Y.
Later in the game when you want to freeze your incoming green cards, you just play this from hand as a reaction and choose to do nothing on-play (since the on-play is "may"), because you likely don't have Copper in play anyway.
The other awkward thing is that you gain the Silver to your hand, but if you played this as a reaction after buying a card, you can't play that Silver.
So I think the reaction works as an interesting decision; but I do think it's weird to have "You may do X to do Y" be used when Y is a penalty.